7 A typing test is taken by 111 people. The numbers of typing errors they make in the test are summarised in the table below.
| Number of typing errors | \(1 - 5\) | \(6 - 20\) | \(21 - 35\) | \(36 - 60\) | \(61 - 80\) |
| Frequency | 24 | 9 | 21 | 15 | 42 |
- Draw a histogram on graph paper to represent this information.
- Calculate an estimate of the mean number of typing errors for these 111 people.
- State which class contains the lower quartile and which class contains the upper quartile. Hence find the least possible value of the interquartile range.